Commissioning and Acceptance Testing of the existing linear accelerator upgraded to volumetric modulated arc therapy

AbstractAimThe RapidArc commissioning and Acceptance Testing program will test and ensure accuracy in DMLC position, precise dose-rate control during gantry rotation and accurate control of gantry speed.BackgroundRecently, we have upgraded our linear accelerator capable of performing IMRT which was functional from 2007 with image guided RapidArc facility. The installation of VMAT in the existing linear accelerator is a tedious process which requires many quality assurance procedures before the proper commissioning of the facility and these procedures are discussed in this study.Materials and methodsOutput of the machine at different dose rates was measured to verify its consistency at different dose rates. Monitor and chamber linearity at different dose rates were checked. DMLC QA comprising of MLC transmission factor measurement and dosimetric leaf gap measurements were performed using 0.13cm3 and 0.65cm3 Farmer type ionization chamber, dose 1 dosimeter, and IAEA 30cm×30cm×30cm water phantom. Picket fence test, garden fence test, tests to check leaf positioning accuracy due to carriage movement, calibration of the leaves, leaf speed stability effects due to the acceleration and deceleration of leaves, accuracy and calibration of leaves in producing complex fields, effects of interleaf friction, etc. were verified using EDR2 therapy films, Vidar scanner, Omnipro accept software, amorphous silicon based electronic portal imaging device and EPIQA software.1–8ResultsAll the DMLC related quality assurance tests were performed and evaluated by film dosimetry, portal dosimetry and EPIQA.7ConclusionResults confirmed that the linear accelerator is capable of performing accurate VMAT

Analysis of low dose level volumes in intensity modulated radiotherapy and 3-D conformal radiotherapy

Purpose: To analyze the low dose volume regions in four facets: Analysis 1: low dose volume regions were compared between 3-dimensional conformal radiotherapy (3DCRT) and intensity modulated radiotherapy (IMRT) plans for each case; Analysis 2: the effect on low dose volume in 3DCRT as the number of fields are increased; Analysis 3: the same effect in IMRT, and Analysis 4: above two analysis were inter-compared between the two modalities. Methods: For this work 18 patients were taken for which both 3DCRT and IMRT plans with varying number of beams were planned using Anisotropic Analytical Algorithm (AAA) in Eclipse 10 Version Treatment Planning System with two to nine beams and five to nine beams, respectively. The plans were analyzed on the basis of conformity index and dose to the critical structures.Results: In Analysis 1, 5 Gy volume region was greater for IMRT than for 3DCRT but the 10 Gy, 15 Gy and 20 Gy volume regions were smaller for IMRT plans. In Analysis 2 and 3 shows that as the number of fields increases the low dose volume regions also increases. In Analysis 4, the effect pronounced due to increase in the beam portals is similar in 3DCRT as well as IMRT. Also it was seen that with same number of beams for both IMRT and 3DCRT, low dose volume region is higher in 3DCRT than IMRT. Conclusion: Low dose volume regions are a major concern in 3DCRT and IMRT plans with multiple beams because of its risk of secondary cancer incidence. This study concludes that by increasing number of beams low dose volume regions increases in 3DCRT and IMRT. It shows that the low dose volume regions are slightly higher in IMRT than 3DCRT, however with proper optimization the volume of tissue receiving 10 Gy, 15 Gy and 20 Gy can be reduced.-----------------------Cite this article as: Ekambaram V, Velayudham R. Analysis of low dose level volumes in intensity modulated radiotherapy and 3-D conformal radiotherapy. Int J Cancer Ther Oncol 2014; 2(3):02032. DOI: 10.14319/ijcto.0203.

Analysis of low dose level volumes in intensity modulated radiotherapy and 3-D conformal radiotherapy

Purpose: To analyze the low dose volume regions in four facets: Analysis 1: low dose volume regions were compared between 3-dimensional conformal radiotherapy (3DCRT) and intensity modulated radiotherapy (IMRT) plans for each case; Analysis 2: the effect on low dose volume in 3DCRT as the number of fields are increased; Analysis 3: the same effect in IMRT, and Analysis 4: above two analysis were inter-compared between the two modalities. Methods: For this work 18 patients were taken for which both 3DCRT and IMRT plans with varying number of beams were planned using Anisotropic Analytical Algorithm (AAA) in Eclipse 10 Version Treatment Planning System with two to nine beams and five to nine beams, respectively. The plans were analyzed on the basis of conformity index and dose to the critical structures.Results: In Analysis 1, 5 Gy volume region was greater for IMRT than for 3DCRT but the 10 Gy, 15 Gy and 20 Gy volume regions were smaller for IMRT plans. In Analysis 2 and 3 shows that as the number of fields increases the low dose volume regions also increases. In Analysis 4, the effect pronounced due to increase in the beam portals is similar in 3DCRT as well as IMRT. Also it was seen that with same number of beams for both IMRT and 3DCRT, low dose volume region is higher in 3DCRT than IMRT. Conclusion: Low dose volume regions are a major concern in 3DCRT and IMRT plans with multiple beams because of its risk of secondary cancer incidence. This study concludes that by increasing number of beams low dose volume regions increases in 3DCRT and IMRT. It shows that the low dose volume regions are slightly higher in IMRT than 3DCRT, however with proper optimization the volume of tissue receiving 10 Gy, 15 Gy and 20 Gy can be reduced.-----------------------Cite this article as: Ekambaram V, Velayudham R. Analysis of low dose level volumes in intensity modulated radiotherapy and 3-D conformal radiotherapy. Int J Cancer Ther Oncol 2014; 2(3):02032. DOI: 10.14319/ijcto.0203.2</p

Integrated scoring approach to assess radiotherapy plan quality for breast cancer treatment

Background: Proposal of an integrated scoring approach assessing the quality of different treatment techniques in a radiotherapy planning comparison. This scoring method incorporates all dosimetric indices of planning target volumes (PTVs) as well as organs at risk (OARs) and provides a single quantitative measure to select an ideal plan. Materials and methods: The radiotherapy planning techniques compared were field-in-field (FinF), intensity modulated radiation therapy (IMRT), volumetric modulated arc therapy (VMAT), hybrid IMRT (H-IMRT), and hybrid VMAT (H-VMAT). These plans were generated for twenty-five locally advanced left-sided breast cancer patients. The PTVs were prescribed a hypofractionation dose of 40.5 Gy in 15 fractions. The integrated score for each planning technique was calculated using the proposed formula. Results: An integrated score value that is close to zero indicates a superior plan. The integrated score that incorporates all dosimetric indices (PTVs and OARs) were 1.37, 1.64, 1.72, 1.18, and 1.24 for FinF, IMRT, VMAT, H-IMRT, and H-VMAT plans, respectively. Conclusion: The proposed integrated scoring approach is scientific to select a better plan and flexible to incorporate the patient-specific clinical demands. This simple tool is useful to quantify the treatment techniques and able to differentiate the acceptable and unacceptable plans

Comparison of peripheral dose measurements using Ionization chamber and MOSFET detector

BackgroundIn radiation therapy, the peripheral dose (PD) – the dose outside the geometric boundaries of the radiation field – is of clinical importance. A metal oxide semiconductor field effect transistor (MOSFET) detector is used to estimate the peripheral dose.AimThe aim of this study is to investigate the ability of a MOSFET dosimetry system to accurately measure doses in peripheral regions of high energy X-ray beams.Materials & MethodsThe accuracy of the MOSFET system is evaluated by comparing peripheral region dose measurement with the results of standard ionization chamber measurements. Furthermore, the measurement of PD using a MOSFET detector helps us to keep the tolerance dose of any critical organ closer to the treatment field within the acceptable limits. The measurements were carried out using a 0.6 cc Farmer type ionization chamber and MOSFET 20 dosimetry system for field sizes ranging from 5 × 5 cm2 to 20 × 20 cm2 at three depths of 1.5 cm, 5 cm and 10 cm in a blue water phantom. PD were measured at distances varying from 1 cm to 30 cm from the field edges along the x axis for the open fields, with collimator rotation and with beam modifiers like 15 degree, 30 degree and 45 degree wedges.ResultsThe results show a good agreement of measured dose by both methods for various field sizes, collimator rotation and wedges.ConclusionThe MOSFET detector has a compact construction, provides instant readout, is of minimal weight and can be used on any surface

Performance characteristics and commissioning of MOSFET as an in-vivo dosimeter for high energy photon external beam radiation therapy

AimIn vivo dosimetry is an essential tool of quality assurance programmes in radiotherapy. In fact, the assessment of the final uncertainty between the prescribed dose and the dose actually delivered to the patient is an effective way of checking the entire dosimetric procedure. Metal oxide semiconductor field effect transistors (MOSFETs) have recently been proposed for use in radiation therapy. The purpose of this work is to study the performance characteristics and to carry out the commissioning of MOSFET as an in-vivo dosimeter for high-energy photon external beam radiation therapy.Material and MethodsCharacterization and commissioning of low sensitivity TN502RD and high sensitivity TN1002RD MOSFETs for entrance and exit dosimetry respectively for application in in-vivo dosimetry in radiotherapy was carried out. The MOSFETs were characterized in terms of reproducibility, short-term constancy, long-term constancy, linearity, angular dependence, energy dependence, source to skin distance (SSD) dependence and field size dependence.ResultsThe reproducibility of standard sensitivity MOSFET is about 1.4% (1 SD) and 1.98% (1 SD) for high sensitivity detectors. The linearity of both MOSFETs was excellent (R2 = 0.996). The response of MOSFETs varies linearly for square fields from 3 × 3 cm2 to 30 × 30 cm2. For beam incidence ranging from ±45° the MOSFET response varies within ±3%. Commissioning of both MOSFETs was carried out in terms of entrance dose calibration factor, exit dose calibration factor, SSD correction factor, field size correction factor, wedge correction factor and shielding tray correction factor. The average calibration factor for low and high sensitivity MOSFET detectors is 0.9065 cGy/mV and 0.3412 cGy/mV respectively. The average SSD correction factors are quite small and vary between 0.968 and 1.027 for both types of detectors for the range of clinical SSDs from 80 cm to 120 cm. The field size correction factor varies from 1.00 to 1.02 for both types of detectors. The wedge and the shielding tray correction factors for both the detectors also show quite small variation. MOSFET characteristics are suitable for in vivo dosimetry of entrance and exit dose measurement relevant to 6 MV treatment.ConclusionIt can be concluded that MOSFET dosimetry's low energy dependence, high sensitivity and immediate readout make it a good replacement for TLD in radiation therapy dosimetry

Commissioning and Acceptance Testing of the existing linear accelerator upgraded to volumetric modulated arc therapy

AimThe RapidArc commissioning and Acceptance Testing program will test and ensure accuracy in DMLC position, precise dose-rate control during gantry rotation and accurate control of gantry speed.BackgroundRecently, we have upgraded our linear accelerator capable of performing IMRT which was functional from 2007 with image guided RapidArc facility. The installation of VMAT in the existing linear accelerator is a tedious process which requires many quality assurance procedures before the proper commissioning of the facility and these procedures are discussed in this study.Materials and methodsOutput of the machine at different dose rates was measured to verify its consistency at different dose rates. Monitor and chamber linearity at different dose rates were checked. DMLC QA comprising of MLC transmission factor measurement and dosimetric leaf gap measurements were performed using 0.13[[ce:hsp sp="0.25"/]]cm3 and 0.65[[ce:hsp sp="0.25"/]]cm3 Farmer type ionization chamber, dose 1 dosimeter, and IAEA 30[[ce:hsp sp="0.25"/]]cm[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]30[[ce:hsp sp="0.25"/]]cm[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]30[[ce:hsp sp="0.25"/]]cm water phantom. Picket fence test, garden fence test, tests to check leaf positioning accuracy due to carriage movement, calibration of the leaves, leaf speed stability effects due to the acceleration and deceleration of leaves, accuracy and calibration of leaves in producing complex fields, effects of interleaf friction, etc. were verified using EDR2 therapy films, Vidar scanner, Omnipro accept software, amorphous silicon based electronic portal imaging device and EPIQA software.[[ce:cross-refs id="crfs0005" refid="bib0005 bib0010 bib0015 bib0020 bib0025 bib0030 bib0035 bib0040"]]1–8ResultsAll the DMLC related quality assurance tests were performed and evaluated by film dosimetry, portal dosimetry and EPIQA.[[ce:cross-ref id="crf0025" refid="bib0035"]]7ConclusionResults confirmed that the linear accelerator is capable of performing accurate VMAT

Dosimetric evaluation of a three-dimensional treatment planning system

The computerized treatment planning system plays a major role in radiation therapy in delivering correct radiation dose to the patients within ±5% as recommended by the ICRU. To evaluate the dosimetric performance of the Treatment Planning system (TPS) with three-dimensional dose calculation algorithm using the basic beam data measured for 6 MV X-rays. Eleven numbers of test cases were created according to the Technical Report Series-430 (TRS 430) and are used to evaluate the TPS in a homogeneous water phantom. These cases involve simple field arrangements as well as the presence of a low-density material in the beam to resemble an air in-homogeneity. Absolute dose measurements were performed for the each case with the MU calculation given by the TPS, and the measured dose is compared with the corresponding TPS calculated dose values. The result yields a percentage difference maximum of 2.38% for all simple test cases. For complex test cases in the presence of in-homogeneity, beam modifiers or beam modifiers with asymmetric fields a maximum percentage difference of 5.94% was observed. This study ensures that the dosimetric calculations performed by the TPS are within the accuracy of ±5% which is very much warranted in patient dose delivery. The test procedures are simple, not only during the installation of TPS, but also repeated at periodic intervals